http://www.css-physics.edu.pl We provide the proof for the 5 D term origin of an excited triplet observed in the recent electron-spin-resonance (ESR) experiments by Noguchi et al. (Phys. Rev. B 66, 094404 (2002)). We have succeeded to fully describe experimental ESR results both for the zero-field g-factor, of 3.35, and the splitting D of 4.90 cm −1 , as well as for the magnetic field applied along different crystallographic directions within the localized electron atomic-like approach as originating from excitations within the lowest triplet of the 5 T 2g octahedral subterm of the 5 D term. In our atomic-like approach the d electrons of the Co 3+ ion in LaCoO 3 form the highly-correlated atomic-like 3d 6 system with the singlet 1 A 1 ground state (an octahedral subterm of the 1 I term) and the excited octahedral 5 T 2g subterm of the 5 D term. We take the ESR experiment as confirmation of the existence of the discrete electronic structure for 3d electron states in LaCoO 3 on the meV scale.

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The total, orbital and spin moment of the Co2+ ion in CoO has been calculated within the quasi-atomic approach with taking into account strong correlations, crystal-field interactions and the intra-atomic spin-orbit coupling. The orbital moment of 1.39 \mu B amounts at 0 K, in the magnetically-ordered state, to more than 34% of the total moment (4.01 \mu B). The same calculations yield for NiO the orbital and total moment of 0.46 \mu B and 2.45 \mu B, respectively. PACS No: 71.70.E; 75.10.D Keywords: 3d magnetism, crystal field, spin-orbit coupling, orbital moment, CoO, NiOComment: 6 pages in tex+3 figs, submitted for PNSXM-03, Venic

The orbital and spin moment of the Νi 2+ ion in NiO has been calculated at 0 K to be 0.54 μB and 1.99 μ$ respectively. Such large orbital moment, more than 20% of the total moment of 2.53 μs, proves the need for the "unquenching" of the orbital moment in compounds containing 3d ions. It turns out that the spin-orbit coupling is indispensable for description of magnetic and electronic properties of 3d-ion compounds.PACS numbers: 75.20.Hr, 71.70.EjThe discovery of the high-temperature superconductivity in the copper oxide has revealed the enormous shortage of our general understanding of the 3d-ion compounds. Namely, the insulating state of La2CuO4 contradicts the standard band-structure result that predicts it to be metal. This dramatic breakdown of the ordinary band-electron theory has been known already for years for 3d-ion monooxides [1][2][3][4][5]. Different reparations do not lead to the consistent picture for 3d-ion systems known as the Mott insulators. At present after announcement of the essential importance of the single-ion effects and many-electron discrete states in description of compounds containing transition-metal atoms of the 3d and 4f groups the fundamental controversy has become the scientific fact [6,7]. In Ref. [6] we have argued that the spin-orbit (s-ο) coupling is essentially important (indispensable) for the description of electronic and magnetic properties of compounds containing 3d ions. The s-ο coupling is largely ignored in the nowadays in-fashion solid-state theories owing to the general conviction about the quenching of the orbital moment and the weakness of the s-ο coupling [1-5] (clearly admitted in Ref.[3], p. 7164). Nowadays ionic systems like LaMnO 3 , LaCοO3 , MgV2 O4 , and NiO are in fashion. Here we will concentrate on properties of NiO.The aim of the present short paper is to report results of calculations of the orbital and spin moment. In NiO the Ni ions are divalent. Their 6 electrons form the highly-correlated electron system with S = 1 and L = 3. The 3 F term is 21-fold degenerated [7,8]. The Νi2+ ion experiences the crystal field, the spinorbit coupling and the intersite spin-dependent interactions. The latter term is approximated by the mean-field approach. The fine electronic structure resulting (963)